From DE 199 10 299 C1 a planetary gear shift mechanism is known, in which an input shaft can be brought into driving engagement with an output shaft by at least one of three planetary gear divided transmissions. Using three respective friction couplings and brakes, five forward gears including one with transmission ratio 1 corresponding to direct throughput can be engaged. By interrupting a particular drive connection between two of the three divided transmissions an additional, sixth forward gear can be obtained. Alternatively, the additional sixth forward gear can be obtained by means of additional auxiliary planetary elements and an additional, outer auxiliary central gearwheel which meshes with the latter, such that the auxiliary central gearwheel can be braked by an additional brake in the sixth forward gear. In a different embodiment this auxiliary central gearwheel also provides a seventh forward gear and an additional reverse gear.
From EP 0 434 525 B1 an automatic multiple-speed transmission for vehicles is known, which consists of several planetary gearwheel assemblies which are engaged by means of friction elements such as clutches and brakes and are usually connected with a starting element subjected to a slip effect and optionally provided with a bridging coupling, such as a hydraulic torque converter or a fluid coupling.
Such automatic transmissions, however, have the disadvantage that all the shift control elements are in the form of multiple-disc couplings or brakes, which take up a lot of structural space and are very costly.
The purpose of the present invention is to provide a transmission of the type described at the beginning, which takes up little space and can be manufactured inexpensively.